This proposal describes experiments designed to characterize the effects of the 120 kD human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gp120) on the intracellular free Ca2+ concentration ([Ca2+]i) in rat hippocampal neurons grown in primary culture. gp120 produces a large (uM) increase in the [Ca2+]i in these neurons. The emerging view that an uncontrolled accumulation of Ca2+ underlies a number of neurodegenerative processes suggests that the gp120-induced increase in the [Ca2+]i in neurons may explain the neuropsychiatric disorders that frequently accompany acquired immune deficiency syndrome (AIDS). The goal of this proposal is to determine how gp120 elevates [Ca2+]i, the role of elevated [Ca2+]i in neurotoxicity and the pharmacology of this process. The mechanism by which gp120 produces an elevation in [Ca2+]i will be determined. The alternatives to be explored are an activation of voltage- sensitive Ca2+ channels directly, an indirect recruitment of Ca2+ channels by producing a membrane depolarization or a diffusible second messenger and the possibility that gp120 acts on microglia to release a neurotoxin. The link between Ca2+ overload and neurotoxicity will be studied. N-methyl-D- aspartate (NMDA)-induced Ca2+ overload and resulting neurotoxicity will be studied to clarify the role Ca2+ plays in the cell death as well as to provide a reference with which to compare the Ca2+ load and toxicity produced by gp120. The pharmacological sensitivity of the pathway linking exposure of the cell to gp120 to an increase in [Ca2+]i will be characterized. Ca2+ channel blockers will be used for the dual purpose of employing them as tools to better characterize the molecular processes which mediate the response as well as for their potential to lessen the degree of Ca2+ overload and hence possible neurotoxicity. The effects of opioids on [Ca2+]i increases and neurotoxicity induced by gp120 and glutamatergic agonists will be studied to evaluate the possibility that opiates increase the sensitivity of neurons to these toxic substances. To achieve these aims membrane ion currents and [Ca2+]i will be measured by employing whole-cell patch-clamp and Indo-1 microfluorimetric techniques both separately and in combination in single rat hippocampal neurons grown in primary culture. These studies will lead to a better understanding of the neurodegeneration frequently associated with AIDS and the effects of drugs of abuse on this process.